1. Field of the Invention
The present invention relates to a computer system having a facility for detection of data abnormalities, more particularly, to a system of detection of abnormalities in data transmission in a data transmission apparatus which transmits data using a data transmission line, and such a data transmission apparatus.
In recent years, the increasing number of computer systems brought on-line has in many cases resulted in a number of computer apparatuses in the system being connected in common through the same data transmission line in a so-called multidrop form.
2. Description of the Related Art
In general, a large number of data transmission apparatuses are connected to a data transmission line. Therefore, an abnormality occurring on the data transmission line causes abnormalities in all the data transmission apparatuses connected to the line. The effect on the computer system as a whole is consequently great.
Among the abnormalities of a data transmission line is the physical disconnection etc. of the signal line. In general, however, the abnormality is caused by a fault occurring in one of the number of data transmission apparatuses connected in common to the data transmission line.
In such a case, a fault occurring at a single data transmission apparatus ends up causing the transmission of data by all the other normal data transmission apparatuses connected in common to the same data transmission line to stop. That is, the other data transmission apparatuses, despite being normal in function, also are made to be abnormal in data transmission operation. In such a case, it is necessary to disconnect the faulty data transmission apparatus from the data transmission line to restore the system from the abnormality.
In this case, however, since all the data transmission apparatuses are connected in common to a single data transmission line, in outward appearance it seems that all the data transmission apparatuses in the system including the faulty data transmission apparatus suffer from abnormalities. Accordingly, it is extremely difficult to specifically determine the faulty data transmission apparatus in the system. As a result, time is taken for the restoration of the system from the abnormal state and therefore the loss in the computer system becomes extremely serious.
The inventor of this application consequently prepared a prototype of a data transmission apparatus to deal with this, described in detail later using the drawings. This data transmission apparatus introduced a transmission/reception control unit for detection of abnormalities and introduced a driver (DV) and receiver (RV) constituting a signal conversion element so as to detect abnormalities in the data transmission. This abnormality detection transmission/reception control unit performed substantially the same function as a transmission/reception control unit for normal data transmission and reception, so the abnormality detection transmission/reception control unit could be realized using exactly the same LSI as the LSI constituting a normal transmission/reception control unit. This LSI, however, included a set of the transmission side circuits and reception side circuits and was considerably expensive. In addition, in the LSI constituting the abnormality detection transmission/reception control unit, use was made of only the reception side circuits, i.e., the transmission side circuits were left unused, so the cost performance was poor. Accordingly, among the pair of the driver (DV) and receiver (RV) provided with the abnormality detection transmission/reception control unit, the driver was left unused and wasted. In the end, there was the problem that the cost of the data transmission apparatus increased and was no longer practical.
Also, when transmitting data from a central processing unit (CPU), the central processing unit both processes the data transmission and receives wrapped data obtained by wrapping the data it has itself transmitted. It is further necessary to check for coincidence of the transmission data and the wrapped data. Therefore, a complicated control program becomes required for the control of the transmission, reception, coincidence checking, and other operations. In addition, the central processing unit has to be given a large processing capability. Therefore, the load on the central processing unit increases and the cost of the central processing unit rises. In this respect as well, it is difficult to realize an inexpensive data transmission apparatus.
Further, when detecting abnormalities in data transmission, human intervention was required to disconnect the abnormal data transmission apparatus from the data transmission line. Accordingly, considerable time was taken for restoration of the overall computer system.